This application claims the priority of German Patent Document 199 54 541.3, filed in Germany, Nov. 12, 1999, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a device for ventilating and venting a fuel tank of a motor vehicle, having a ventilating structure which compensates the pressure in a fuel tank.
In a fuel tank of a motor vehicle it is possible for gas contained in the fuel tank to be subjected to fluctuations in pressure, for example because of fluctuations in the temperature of the surroundings, the fluctuations in pressure requiring the pressure to be compensated. Furthermore, during the filling or emptying of the fuel tank, a positive pressure or, respectively, a negative pressure is produced which likewise has to be compensated. The pressure in the fuel tank is generally compensated by means of a device for ventilating and venting the fuel tank.
The devices known in practice for this conventionally have a vent which is arranged in the upper region of the fuel tank and is connected to a filter element, the filter element cleaning the gas flowing out of the fuel tank.
A problem with these devices is that during extreme driving or operating states, for example when cornering sharply, when driving uphill and downhill or when the vehicle is on its roof, for example in the case of an accident, the fuel level in the fuel tank rises in such a manner that it is possible for fuel to escape out of the fuel tank through the vent. The fuel is able to pass via the vent to the filter element and to impair or damage the functioning thereof. There is also the risk of fuel escaping from the fuel tank and contaminating the surroundings of the vehicle.
The fuel tanks which are conventionally used are preferably arranged in the underbody of the vehicle, for space reasons, and so fuel tanks having the lowest possible overall height and a large area are generally provided. In the case of fuel tanks designed in such a manner, the problem described above is further exacerbated, since the gas space formed above the fuel level is very low in these fuel tanks and so it is possible for fuel to escape through the vent even in the event of a small static or dynamic rise of the fuel level in the fuel tank.
In order to prevent the fuel from escaping from the fuel tank through the device for ventilating and venting, the device is provided in an additional container above the fuel tank which is connected to this container via a line. The fuel level in the fuel tank can therefore rise further without immediately reaching the vent. Particularly during extreme driving and operating states, an escape of fuel is therefore made more difficult because of the correspondingly higher position of the vent.
A device of this type is disclosed in German patent Document No. DE 196 05 922 A1. The device comprises an operating ventilating structure which is arranged in a container, is arranged above the fuel tank and is connected via a vent line to the fuel tank. The operating ventilating structure is also connected to a refuel-venting arrangement which is arranged in a filler neck of the fuel tank.
The operating ventilating structure which is arranged outside the fuel tank is connected via a connecting line to a filter element. The connecting line can be closed by a float valve. When the tank is filled to an appropriate level, a closing body which is connected to the float can be positioned in a sealing manner against a valve seat of the float valve, with the result that fuel is unable to escape through the connecting line to the filter element. After the fuel level has sunk again, the float of the valve is lowered again, thus enabling ventilation and venting of the fuel tank to take place.
In the case of the known device, in addition to the fuel tank, installation space for the device is required in order to arrange the latter together with the fuel tank on the vehicle. Because of the spatial separation of the fuel tank from the device for ventilating and venting, pre-assembly of the fuel tank or of the complete fuel system is made difficult or is impossible.
Moreover, connecting lines to the fuel tank and to other components, for example to the refuel-venting means, are required. As a result, a plurality of points of separation between the individual components which are connected to one another are necessary and these, like the components themselves, can cause emissions of fuel.
An object of the invention is to provide a device for ventilating and venting a fuel tank of a vehicle, the said device being further improved with regard to its ease of installation and with regard to possible emissions of fuel.
According to the invention, this object is achieved by a device for ventilating and venting a fuel tank of a motor vehicle, having a ventilating structure which compensates the pressure in a fuel tank, wherein a separating container for separating fuel from a gas contained in the fuel tank is provided, and wherein the ventilating structure is connected to the separating container, the ventilating structure and the separating container being arranged in the fuel tank.
The device according to the invention affords the advantage of emissions of fuel from the fuel tank being effectively prevented, since all of the components of the device, for example the ventilating structure, which can also include a refuel-limiting valve, and the separating container, are arranged within the fuel tank. In the device according to the invention, a connecting line between the separating container and the ventilating structure is also arranged in the fuel tank, with the result that possible leakages from the components of the device which are arranged within the fuel tank do not lead to the fuel escaping or to its emission into the environment.
The novel arrangement of the device in the fuel tank also has the advantage that the fuel tank or the entire fuel system having the device can be pre-assembled, which simplifies the final assembly with regard to working steps which arise.
In the device according to the invention, provision is made for the gas which is fed into the separating container from the ventilating structure and, for example, from a refuel-limiting valve, to be separated from the fuel which is transported with or entrained by it. This can be achieved by the entrained fuel being guided into the lower region of the separating container and by the gas being guided into the upper region of the separating container for the purpose of being conducted further to a filter element which cleans the gas.
The device according to the invention has just one connection to the filter element, which removes the gas from the fuel tank and feeds ambient air to the fuel tank. As a filter element, use can be made, for example, of an activated carbon filter arranged outside the fuel tank. Alternatively, the filter element could also be arranged in the fuel tank.
According to an advantageous development of the invention, a gas inlet and a gas outlet are provided in the separating container, these being arranged in the upper region of the separating container and being separated from each other by a splash guard. Because of the force of gravity, the fuel transported together with the gas is able to run or drip down along a wall of the separating container or along the splash guard to the lower region of the separating container and is able to be returned to the fuel tank by means of a fuel-removing device situated at this location. In contrast, the gas remains in the upper region of the separating container and is passed on via the gas outlet to the filter element.
Alternatively, it is also contemplated for other separating bodies, for example cyclones or the like, to be provided. However, the separating container has the advantage of being of a structurally simple design and therefore of being cost-effective.
The secure screening of the device according to the invention by the fuel tank facilitates the use of conventional, cost-effective components as valves in which a certain amount of leakage can be tolerated.
The use of the device according to the invention is particularly advantageous in the case of fuel tanks which are of flat construction because in this case the volume of gas above the fuel level is very low, and it is virtually impossible, without separating the fuel from the gas, to prevent fuel from passing into the filter element using a known device.